1. Field of the Invention
The present invention relates to an active vibration controller.
2. Description of the Related Art
In conventional passive-type vibration absorbers, an eigenvalue of the vibration absorber is uniquely determined because a physical property of the configuration elements is fixed. Accordingly, when a frequency of the disturbance vibration agrees with the eigenfrequency of the vibration absorber, a high damper effect is given. However, when the frequency of the disturbance vibration is different from the eigenfrequency even slightly or when the frequency of the disturbance vibration varies as time passes, i.e., in an unstable state, the damper effect of the dynamic absorber cannot be fully given. Regarding this problem, a method of designing an optimal tuning and optimal damping to keep a damping effect over a certain frequency band is known. However, its damping effect is insufficient.
On the other hand, as a counter part of the passive type of damping device, an active mass damper is known. In this method, an actuator for forcibly vibrating a mass is installed in addition to the mass element. This provides a high damping effect irrespective of stable or unstable in frequency because, theoretically, an arbitrary damping force can be generated though any disturbance is applied. However, there are problems in that a device to directly apply outer energy becomes complicated and that a control system designing become necessary to avoid unstableness, and that a cost is high. Further, there is a semi-active type of a control method which is an intermediate type between the passive type and the active type. In the semi-active type of damper, a physical characteristic of one of configuration elements, which is originally fixed in the passive type system, is made variable with some means to have variability in the physical characteristic in the system. This enables the system control while the variation due to a disturbance is tracked to some extent. The semi-active type of control method has advantageous effects such as a control performance close to the active type of control method with reliability and stability derived from the passive elements and provides a device at a cost which is lower than that of the active type of control.
WO 2012/026332 discloses a configuration for varying an elastic modulus of a magnetic elastic body by application of a magnetic field generated by an exciting coil using a configuration in which the exciting coil is arranged around an outer circumference of a magnetic elastic body of which elastic modulus can be changed by application of a magnetic field by the exciting coil.
WO 2012/026332 disclosed a technology in which a stiffness of a magnetic viscoelastic elastomer is changed by application of a magnetic field to the magnetic response-type elastic body (magnetic viscoelastic elastomer) is changed. When the magnetic field is applied to the magnetic viscoelastic elastomer, the magnetic field is applied to the magnetic viscoelastic elastomer uniformly and varies the stiffness of the magnetic viscoelastic elastomer in accordance with the application intensity of the magnetic field. The magnetic viscoelastic elastomer can be produced by dispersing magnetic particles in, for example, rubber.
However, it was forced to distribute the magnetic particles in a part which does not largely contribute to change the stiffness of the magnetic viscoelastic elastomer, it is necessary to increase an amount of the magnetic particles included in a base material to increase a variation in stiffness of the magnetic viscoelastic elastomer. This may invite an increase in a lower limit of the base stiffness of the magnetic viscoelastic elastomer.
Further, the magnetic field cannot be applied to the magnetic viscoelastic elastomer efficiently because the magnetic field may be applied to the part of the magnetic viscoelastic elastomer in which the magnetic particles are not distributed, so that it was not performed to apply the magnetic field to the magnetic viscoelastic elastomer efficiently. Accordingly, it was forced to increase a magnitude of the generated magnetic filed by increasing the applied current to generate the magnetic field. In addition, there is a problem in that an effect of the magnetic viscoelastic elastomer as a spring in a dynamic damper may be low because the magnetic viscoelastic elastomer has a large attenuation characteristic.